The invention relates to a method for non-contact measurement of the deflection of a road or a rail, and equipment for the execution of this measurement.
The measuring of the movement of train rails and roads under load is of particular interest, in that it is hereby possible to be able to evaluate their carrying capacity, condition, durability and, in certain cases, also direct faults in the surface or the underlying structure, so that repair work can be initiated in the most expedient places.
It is known to measure the deflection of a road, e.g. making use of a so-called Benkelmann's beam which is positioned on the road, after which a vehicle or the like with a heavy load, e.g. 5-15 tons, is driven closely past the measuring beam and the deflection is measured. This is a relatively precise but very slow method for the measurement of the deflection of roads. Vehicles are constructed with such a measuring beam which can intermittently measure the section of a road by movement of the measuring beam, though only at a maximum of 5-10 km/h. When such measurements are to be carried out, it is thus necessary to give serious consideration to the question of security, in that such a slow-moving vehicle is of great danger for the traffic, which means that the measurements must often be shelved for implementation during periods of light traffic, and also while making use of at least one accompanying vehicle with warning signs etc. which, of course, considerably increases the costs of the measurements.
Furthermore, various methods have been developed whereby the road surface is influenced by a falling weight or the like, and deflection-like measurements can be made. These methods are also very slow and provide measuring results only at intervals, i.e. they do not provide continuous measurements of the road surface.
From the Swedish publication no. 457.807 there is known a vehicle with a load, e.g. of 5-15 tons, and on which at least two range finders are mounted which measure the distance to the road surface, e.g. laser-beam measuring devices, one of which measures the distance to the unloaded road surface (reference), while the other measures as closely as possible to the point at which the road surface is influenced by the loaded wheel. If the equipment is suitably adjusted, such a vehicle is able to be driven forwards at a reasonable speed. The difference between the two distance measurements, corrected for angular errors etc., is subtracted, and the difference constitutes the deflection, i.e. the depression due to the load. Since the deflection during normal loading on a vehicle wheel, i.e. of 5-15 tons, is in the order of 1-4 mm, it will be obvious to those familiar with the art that such difference measurements will be encumbered with even much greater errors, in that the depression which is to be measured is in the same order as the irregularities which are normally to be found in the road surface. Consequently, this method has not been found to be successful for road measurements. On the other hand, it could possibly be used for the measurement of the deflection of a railroad track.